This invention relates to an apparatus for controlling the introduction of air into an exhaust pipe, for introducing air into an exhaust pipe of an internal combustion engine so as to purify exhaust gases. A catalyst is generally provided in an exhaust passage so as to purify exhaust gases from an internal combustion engine. Immediately after the starting of an internal combustion engine in which the catalyst temperature is low and purification efficiency is low, it has been the conventional practice to introduce air into an exhaust pipe upstream of the catalyst so as to promote the oxidation of HC, CO and the like in the catalyst, thereby accelerating the temperature rise of the catalyst and enhancing the purification efficiency.
FIG. 46 shows a configuration of a conventional apparatus for controlling the introduction of air into an exhaust pipe of an internal combustion engine, in which reference numeral 1 denotes an internal combustion engine; 2, a transmission; 3, an intake pipe; 4, an exhaust pipe; 5, a catalyst disposed in the exhaust pipe 4; 6, a throttle valve disposed in the intake pipe 3; 7, an air cleaner disposed in an inlet portion of the intake pipe 3; 8, an air pump mounted on the internal combustion engine 1; 9, an air introducing pipe for introducing air to the exhaust pipe 4 upstream of the catalyst 5 by means of the air pump 8; and 10, a check valve disposed in the air introducing pipe 9 for preventing the reverse flow of exhaust gases from the exhaust pipe 4.
Next, a description will be given of the operation of the conventional apparatus. The air pump 8 introduces air into the exhaust pipe 4 via the air introducing pipe 9 in correspondence with the rotation of the internal combustion engine 1, and the air introduced to the interior of the exhaust pipe 4 reacts with exhaust gas components CO and HC in the exhaust pipe 4 and in the catalyst 5 and converts the same into H.sub.2 O and CO.sub.2, thereby effecting the purification of the exhaust gases. The introduction of air into the exhaust pipe 4 is started simultaneously with the on operation of an unillustrated starter switch, as shown in FIG. 47. The amount of air introduced at this time is substantially fixed in terms of time, as shown in FIG. 48, and the temperature of the introduced air is that of the atmospheric air.
FIG. 49 shows a configuration of another conventional apparatus, in which reference numeral 11 denotes a control valve disposed in the air introducing pipe 9 for adjusting the amount of air to be introduced; 15, a heater for heating the air passing through the air introducing pipe 9; 16, a relief valve attached to the control valve 11; and 12, a controller for controlling the control valve 11 and the heater 15. The other configuration is the same as that of FIG. 46.
Next, a description will be given of the operation of the conventional apparatus shown in FIG. 49. At the same time as an unillustrated key switch is turned on, the control valve 11 opens the passage by being controlled by the controller 12. While the internal combustion engine is cranking (when the starter switch is turned on), the air pump 8 is driven by the internal combustion engine 1 and introduces the air into the exhaust pipe 4 via the air introducing pipe 9, the control valve 11, the heater 15, and the check valve 10. The air introduced into the exhaust pipe 4 reacts with the exhaust gas components HC and CO in the exhaust pipe 4 and the catalyst 5, thereby effecting the purification of the exhaust gases. FIG. 50 shows a chart of operation at this time, in which the starter switch is also turned on simultaneously as the key switch is turned on, the internal combustion engine 1 also starts to rotate simultaneously therewith and drives the air pump 8, thereby introducing an amount of air corresponding to its number of revolutions into the exhaust pipe 4. At this time, the air is heated by the heater 15, and the temperature of the air at the outlet of the heater 15 changes with time, as shown in FIG. 51.
In addition, FIG. 52 shows still another conventional apparatus, in which reference numeral 8a denotes an air pump of an electrically controlled type disposed in the air introducing pipe 9; and 22, an air flow sensor for measuring the amount of air intake. The operation is similar to that of the above-described conventional apparatuses.
FIG. 53 shows a configuration of a further conventional apparatus, in which reference numeral 46 denotes an air-fuel ratio sensor disposed in the exhaust pipe 4 for detecting the air-fuel ratio of the exhaust gases, and the other configuration is the same as described above. Although the operation is similar to that described above, the air-fuel ratio sensor 46 detects the air-fuel ratio of an air-fuel mixture of the introduced air and the exhaust gases at the time of the introduction of the air, and is capable of controlling the air-fuel ratio on the basis of it.
The conventional apparatuses for controlling the introduction of air into an exhaust pipe of an internal combustion engine are arranged as described above, and the normal-temperature air is introduced into the exhaust pipe 4 immediately after starting when the exhaust gas temperature is low, so that there has been a problem in that the temperature of the exhaust gases is further lowered by the introduced air, thereby resulting in a decline in the efficiency of purifying the exhaust gases in the catalyst 5.
In addition, since the air is introduced into the exhaust pipe 4 simultaneously as the starter switch is turned on, the air passes through the interior of the heater 15 before the heater 15 reaches a predetermined temperature, and the speed of temperature rise of the heater 15 is delayed. Hence, there has been a problem in that the efficiency of purifying the exhaust gases in the catalyst 5 declines.
Furthermore, the amount of air introduced is constant irrespective of the operating condition of the engine and the type and condition of the catalyst 5, so that there has been a problem in that an optimum purification efficiency cannot be attained.
In addition, since the high temperature of the exhaust gases from the exhaust pipe 4 acts on the check valve 10, the heater 15, and the control valve 11 disposed in the air introducing pipe 9, it is difficult for these members to operate properly for long periods of time, which in the long run resulted in the decline in the purification efficiency.
With the conventional apparatuses, the introduction of air is commenced simultaneously with starting and, as shown in FIG. 54, the introduction of the air into the exhaust pipe 4 is continued even after the passing of a point of time (point A) when the catalyst inlet temperature (solid line) and the catalyst outlet temperature (dotted line) in the exhaust pipe 4 agree with each other. As a result, the temperature rise of the catalyst 5 becomes saturated, so that a further improvement in the efficiency of purification by the catalyst 5 is hampered. At the same time, the condition becomes one in which oxygen is in a state of oversupply, and the action of reducing nitrogen oxides by means of the catalyst 5 declines, so that there has been a problem in that the amount of nitrogen oxides emitted increases.
In addition, since the air is introduced to the upstream side of the air-fuel ratio sensor 46, there has been a problem in that the air-fuel ratio of the exhaust gases alone cannot be detected accurately, thereby making it impossible to effect fuel control accurately.